Phase-Lock Loops (PLLs) are circuits that may be used to recover clock signals from serial data-bit streams and/or to generate re-timed data. As operating speeds of clock and data recovery circuits increases, the design of PLL components (e.g., a voltage-controlled oscillator (VCO), a phase-detector (PD) and/or a divider) becomes more complicated and consumes more power. Some architectures use multiple phases of a lower-rate clock but feature non-linear characteristics or reduced linear range.
Referring to FIG. 1, a circuit 10 is shown illustrating a conventional data recovery circuit. The circuit 10 generally comprises phase detector 12, a phase frequency detector 14, a divider 16, a VCO 18 and a CPF 20.
The VCO 18 generates a full-rate clock which is divided by "N" by the divider FBDIV 16. The divided down clock signal CLK_DIV is presented to the phase-frequency detector 14. The PFD 14 also receives a reference clock signal REFCLK_IN which is typically a divided by N version of the data signal. The PFD 14 compares the signals REFCLK_IN and CLK_DIV and generates a pump-up and a pump-down signal. The pump-up and pump-down signals are presented to the charge-pump/filter 20 through a multiplexer controlled by a signal LLC. The signal LLC controls the "locking" of the circuit 10 to the signal REFCLK_IN or the signal DATA. When the circuit 10 is frequency locked to the signal REFCLK, the multiplexer 22 is switched to select the signal DATA (through the PD 12) for the closed loop by using the signal LLC. The close loop-with the PD 12 then locks the signal DATA and generates recovered data and clock signals. This implementation requires the use of a full-rate PD 12 and a full-rate VCO 18. The VCO 18 generates a single phase of the clock. The divider FBDIV 16 is also a full-rate single-phase divider.
The circuit 10 has the disadvantage that is (i) requires full rate components such as the phase-detector and the VCO, (ii) requires a linear full-rate phase-detector, and/or (iii) has a full-rate operation that implies higher power components are required.